Spark plug



Patented Feb. 12, 1946 SPARK PLUG Frederick I. McCarthy, Forest Hills,and Charles Schandler, New York, N. Y.

Application December 10, 1942, Serial No. 468,540

3 Claims.

This invention relates to spark plugs, and more particularly to the typein which ceramic portions are utilized. In spark plugs of this typethere has been found in the use thereof, a great deal of difficulty inthat the ceramic structure would, due to its inherent strains andstresses, be subject to breakage during the use of the spark pluparticularly in such cases where coneshaped washers are utilized for thepurpose of securing a tight fit, which tight fit has for its object toprevent leakage of gases from the cylinder.

The object of this invention is to provide an improved spark plug whichmay be constructed from ceramic material of such a shape as to be freefrom harmful internal strains and stresses at the point where thelocking action is provided to prevent the leakage as aforesaid. Thesimplest form of ceramic member is a plain hollow cylinder in that allof the strains and stresses in the concentric inner and outer walls areequalized. A more refined form of such a ceramic member is to provideshoulders upon such cylindrical member, which shoulders have the purposeof functioning with the steel shells of the spark plug to limit theposition of the ceramic member. Also, such an improved cylindricalceramic member may be used to determine the amount of space desirablefor the spark or arcing, Here again, when such locking portions are of acylindrical shape the internal strains and stresses resulting from theuse of the same are neutralized or balanced and the ceramic portion ofthe spark plug is then not subject to harmful strains tending towardbreakage as heretofore.

In-order to avoid such breakage at that portion of the ceramic memberwhich is subjected to a sealing action to prevent leakage, thisinvention contemplates the combination with the aforesaid ceramic memberof a compression member which is made from powdered copper or any othersuitable kind of powder material or materials which when subjected to ahigh pressure brings about the coherence of the particles of the powderinto a single solid mass. This mass has a large surface area compared todevices heretofore in use and the compression forces passing throughthis solid mass and acting upon the cylindrical exterior of the ceramicmember divide the action of the forces equally upon the unit area so asto distribute the force and will bring about an absolutely secureholding and sealing action.

For this purpose my invention consists of a spark plug in which there isa cylindrical ceramic member surrounded by a chamber in which powderedmaterial is supplied and which powdered material after it has beensubjected to a very high pressure, enters the solid state and therebycauses the compression forces to exert themselves upon the longitudinalwall of the Outer chamber and upon the wall opposite thereto, namely,the exterior cylindrical part of the ceramic member. While such powderedmaterial is under such applied pressure it acts like a fluid and entersthe interstices of the outer wall of the ceramic member, and upon therelease of the pressure, it becomes a solid mass.

The invention also consists in providing this cylindrical member ofceramic material with cylindrical shoulder portions to limit themovement of the cylindrical ceramic member in respect to the other partsof the spark plug, and in the further contemplated invention saidcylindrical shoulders serve the further function of limiting the amountof space necessary for the sparking action. In certain cases theshoulder of the ceramic member may serve to insure a balanced heatdistribution between the positive spindle and the negative lower shell.Among other things a prevention of fouling results.

This invention will be more fully described hereinafter, embodimentsthereof shown in the drawings, and the invention will be finally pointedout in the claims.

In the accompanying drawings:

Fig, 1 is a longitudinal central section of a spark plug presenting oneembodiment of this invention;

Fig. 2 is a longitudinal vertical section of another embodiment of thisinvention;

Fig. 3 is a longitudinal vertical section of still another embodiment;

Fig. 4 is a longitudinal vertical section of another embodiment;

Fig. 5 is a fragmentary enlarged portion of parts of the structure shownin Fig. 4 showing the functioning of the parts therein shown, and

Fig. 6 is a horizontal section taken on line H ternal screw thread itand upon the lowermost free end of this exteriorly screw threaded por-'tion it, one of the sparking members II is suitably secured thereto,preferably welded. The member It has a bore I1, and aninternallyextending shoulder is which has a sub-calibered bore to the bore i1.About the shoulder II the member ID has a bore IQ of substantially thesame diameter as the bore l1. Into the internal threads is of theextension l2 another metallic cylindrical hollow member with externalthreads is fitted and this member 20 has at its free upper end externalthreads 2|. Within the member 20 at its central portion is a centralmember 22 which extends downwardly and is of electrically conductingmaterial and has at its lowermost end 24 a spark head 2|, whichembodiment is frusto-conical in shape and enables this member 25 to bein spacial relationship to the other sparking member it which iscircularly disposed around the member 23, and it is over the air-gaptherebetween that the sparking takes place. The are member 28 issuitably secured to the steel member 22 by welding and this member 22has a bore which is filled with a copper rod 28. with the exception ofthe cylindrical bore It, the parts described are known and are common toall of the embodiments shown with the exception of the embodiment ofFig. 3 in which the spark member 28 is of an extension type with acurved surface 2! in the nature of a button, the peripheral portions ofwhich cooperate with the ends 30 for the passage of the spark over theair-gap portion 2i. This latter construction is also known.

The improvement consists in surrounding the central member 22 with acylindrical ceramic member having a bore 32 which is concentric with theexternally cylindrical surface 33, and the bore 32 and the externallycylindrical surface 23 are co-extensive throughout the length of thisceramic member 25. This ceramic member ll of Fig. 4 extends from thewasher end 36 to the spark end 25 and huggingly engages the centralmember 22 and at the same time the shoulder portion ll of the casing,the casing itself having the interior bore 19 of larger diameter thanthe diameter of the exterior surface of the ceramic member 25. The spacethen formed between the outer surface 23 of the ceramic member I! andthe bore 18 of the casing and the upper surface of the shoulder portionfl is then filled with a copper powder and when so filled is subjectedfirst to a tamping action more or less generally applied and thereafterto a stronger pressure, in fact to a very high compression action so asto convert these particles of the powder after acting like a fiuid intoa solid member in a manner well known with the cooperation of heat as inpowder metallurgy. Instead of copper powder some other powder ofsuitable material may be used. The importance here is a secure fitagainst any possible leakage of gases, oil, etc., which may affect theoperation of the spark plug. The combination of this kind of a sealingaction with the ceramic member of cylindrical shape has the advantagethat the compression forces are distributed over a large area instead ofbeing applied to a small area whereby breakages of the ceramic membertake place. The, distribution of such compression forces over theexternal portion of a cylinder has the further advantage that due to theinherent resiliency of a hollow cylindrical ceramic member a portionthereof may be'very slightly bent by such high pressure and thereby theinternal bore of the cylindrical ceramic member forced tightly againstthe internal member 22. An exaggerated view of this is shown in F18. 5.It is believed also that such a distribution of compression forcesprobably have an effect upon the molecular construction of the ceramicmember under such pressure whereby a greater compactness of the ceramicmember is obtained, again acting as a sealing action or breaking actionagainst any forces tending to bring about leakage.

From the simplest form of cylindrical ceramic member with an internalbore concentric with its exterior as in Figure 3. this cylindricalmember Ila may be provided with a shoulder portion 40 resting upon theupper surface ll of the internal shoulder of the casing In such as shownin Fig. 3. Thereby a limitation of movement of the cylindrical ceramicmember Ila in Fig. 3 is brought about. In this embodiment of Fig. 3 theceramic cylindrical member "a has an extension llb which enters into thespark button 28. The spark button or sparking member 28 has a memberrecess into which this extension enters, and the insulating member Ilaextending from said recess beyond the spark gap acts as an insulatingbarrier behind the spark gap, and electrically separates the casing IIfrom the conducting member of the sparking member. In the embodiment ofFig. 3 the internal bore II is longitudinally longer than that shown inFig. 4 and the feeding of the powdered material is from the top, as isalso the case in the embodiment of Fi 4.

In the embodiment of Fig. 2 the cylindrical ceramic member "c has anextension 42 which has a larger size bore than the bore of the member"c. This member ll extends to the extreme upper end of the casing 2| andis suitably secured thereto by an internal washer 42 or the like. Theupper end of the central member 22 is suitably secured to the ceramicmember ll by upsetting the member 22 as shown by is after a screwthreaded washer N has been applied to the external screw threadedportion of the member 22. This ceramic member "0 has a shoulder portionII which again is seated upon the shoulder portion ll of the casing IIand thereby the movement of the ceramic member He is controlled. Theceramic member Ilc then extends with its externally subcalibered portiondownwardly to contact with the sparking end 2' which is offrustro-conical shape as in Fig. i. In this embodiment the filling ofthe material takes place from the bottom up instead of from the top downs in the other embodiments. For this purpose the internal bore wall IIis provided in the casing I O and the extended annulus of compactedpowder forced into a solid as indicated by ll, is provided. [is stated,instead of copper powder, any other suitable powder which has certainspecial qualifications and which will compact itself into a solid may beused. Of course in providing a copper filling in Figure 2. this is donebefore the sparking member II is affixed to the casing as by welding orthe like. and after the filling II has been completed this sparkingmember is applied. In Figure 2. the ceramic is one piece from thesparking tip to the washer at the top of the upper shell, and the uppershell is not secured to dthe ceramic, except by the fastening at the enReferring now to Fig. l, in which the ceramic member "d has acylindrical bore and acts with an externally cylindrical portion 4!which is made part of the shell 2. and which extends to the uppermostend of the shell and downwardly to form one wall 48 of the fillingchamber and has a thickness of wall so as to rest upon a shoulder 49 ofthe casing Ill. The ceramic member 350 distribute heat so as to bringabout a substantial uniformity of heat between the positive spindle andthe negative lower shell during the sparking action. It will be notedthat the cylindrical annulus or collar 50 of the ceramic member 35d atthe shoulder portion serves to lock the ceramic member 35d against anyupward movement, and the shoulder portion 49 of the shell acts to lockthe cylindrical ceramic member 35d against a movement in the oppositedirection. Thus the ceramic member is so shaped as to look into asubstantiall unmovable position. It is subjected due to the compressionforces of the filling member 45 to a. sealing action of such a kind asbefore described as to prevent any leakage. The shell 20 may beunsecured with the enclosed ceramic lining member 42 while the ceramicextension is part of the shell and may be removed therewith. The twoceramic cylinders 35d and 41 can be cemented together. In such a case,as also with the embodiment of Fig. 2, a weather proof spark plugresults due to its complete sealing from moisture or other weatherconditions. This eliminates the possibility of any interiordeterioration in the upper shell compartment particularly preventingelectrical leakage due to the moisture. In Fig. 2 the ceramic member 350is integral from end to end of the shell.

The parts are assembled as described, and in view of their respectivecoeflicients of expansion, the steel central member 22 has a tolerancespace with the bore of the porcelain member surrounding it, and theexterior of the porcelain has a tolerance with the bore of the memberID, so that on expansion of the respective parts these tolerances aretaken up. In respect to the expansion of the filling material 45, thisis taken up by the porcelain in the manner indicated by Fig. 5, in thedotted curved line there shown.

From the foregoing it therefore appears that the invention consists ofthe combined action of an externally cylindrical internallycylindrically bored ceramic member extending substantially from thesparking end to the other end of a spark plug thus insuring insulatingqualities throughout combined with a pocket in which a sealing action isprovided by providing such a pocket with powdered material andsubjectingthis powdered material to high pressures to transform it intoa solid. And the invention also consists in the particular shape of sucha cylindrical member whereby such a ceramic member is locked in positionagainst any displacement movement.

It will have noted that this invention deals with several patterns ofceramic insulations adaptable to certain styles of spark plug shellsusing pressed powders as a method of sealing any or all of theparticular patterns to the shells themselves.

The various styles of ceramic patterns have been planned so as to affordmaximum heat deliverance from those portions of the plug which normallybecome too hot. They are also dema so that with the use of pressedpowder they become mechanically rigid and lose none of their electricalor thermal qualities.

Having thus described our invention and the embodiments thereof, we donot wish to be limited to the particularities thereof, and desire toinclude such changes as may be made without departing from the spirit ofour invention as defined in the appended claims.

What we claim is:

1. In a spark plug consisting of a metallic casing having externalattaching means and an internal circumferential shoulder formingcylindrical bores within the casing, and a central cylindricalconducting member having a sparking end and extending from that end tothe other end of the spark plug; a hollow cylindrical ceramic sleevemember with inner and outercylindrical surfaces extending from thesparking end of the central member to said other end of the spark plug,the internal diameter of the bore of said ceramic member being equal tothe external diameter of said conducting member, and the externaldiameter of the ceramic member being equal to one of the bores of saidcasing, the external diameter of the ceramic member being substantiallythe same throughout its length, said casing having walls adjacent saidshoulder portions spaced from said ceramic member to form a fillingchamber, said conducting member extending above and below said chamber,and metallic material formed of compressed powder in said fillingchamber having inherent compression forces to prevent leakage betweensaid filling material and the walls of the casing and the external wallsof the ceramic member, respectively, such forces resulting fromconverting the powder into a solid under pressure, and such forces beingdistributed over an area along the external cylindrical part of saidceramic member between the ends thereof and pressing it radiallyinwardly preventing the axial movement of the ceramic member.

2. In a spark plug'consisting of a metallic casing having externalattaching means and an internal circumferential shoulder formingcylindrical bores within the casing, and a central cylindricalconducting member having a sparking end and extending from that end tothe other end of the spark plug; a hollow cylindrical ceramic sleevemember with inner and outer cylindrical surfaces extending from thesparking end 'of the central member to said other end of the spark plug,the internal diameter of the bore of said ceramic member being equal tothe external diameter of said conducting member, and the externaldiameter of the ceramic member being equal to one of the bores of saidcasing, the external diameter of the ceramic member being substantiallythe same throughout its length, said casing having walls adjacent saidshoulder portions spaced from said ceramic member to form a fillingchamber, said conducting member extending above and below said chamber,metallic material formed of compressed powder in said filling chamberhaving inherent compression forces to prevent leakage between saidfilling material and the walls of the casing and the external walls ofthe ceramic member, respectively, such forces resulting from convertingthe powder into a solid under pressure, and such forces beingdistributed over an area along the external cylindrical part of saidceramic member between the ends thereof and pressing it radiallyinwardly preventing the axial movement of the ceramic member, and anexternal shoulder portion on said ceramic member of cylindrical shapeand of a diameter slightly larger than that of the cylindrical ceramicmember, coacting with the shoulder of the casing to prevent the movementof the ceramic member in one direction of the casing.

3. In a spark plug having a casing, a cylindrical insulating sleevemember in said casing having a cylindrical bore, said insulating memberextending from end to end of the spark plug in 10 an integral piece,with an outer configuration of cylindrical shape concentric with itsbore, a cylindrical conducting member of an external di-

